The younger the person is when the disease appears, the greater the risk for disability and early death. Those who develop the disease early can have vision problems that progress to blindness, and problems with mental function that get worse. If the disease starts in the first year of life, death by age 10 is likely.

If the disease occurs in adulthood, symptoms will be milder with no vision loss and a normal life expectancy.

Possible Complications:

Vision impairment or blindness (with the early-onset forms of the disease)

Mental impairment, ranging from severe developmental delays at birth to dementia later in life

Rigid muscles (due to severe problems with the nerves that control muscle tone)

The person may become totally dependent on others for help with daily activities.